With the prevalence of mobile devices nowadays, amplifier devices are used in communication modules in great quantity. Due to the fact that the power-gain curve and power-phase curve of an amplifier device tend to be non-linear when they reach a certain level, amplifier devices are limited in power usage. Though the approaches of reducing the power or introducing a pre-distortion circuit may be utilized, the complexity of circuit design and cost would increase correspondingly. Moreover, the linearity of an amplifier device varies according to the input signal, voltage source or temperature, so that if a pre-distortion circuit is utilized as previously described, different control factors need thus be considered, and the circuit design would also become more complicated.
Therefore, providing an amplifier device with simple circuit and capable of self-adjusting linearity becomes a critical issue.